The denture art has long known of clasping devices, usually a metal clasp with protruding ends which embrace an abutment tooth, to secure a denture in place. These conventional clasping devices are incapable of forming a seal with the abutment teeth they embrace. As a result, food can become lodged between the clasp and the tooth, causing decay and other problems. As well, metal clasps are likely to damage the abutment teeth and the tissue of a user's mouth, causing injury and pain.
More recently, dentures have been formed with gasketed apertures through which the anchoring teeth pass when the denture is inserted in the user's mouth. Such dentures and methods of making the same are described in U.S. Pat. No. 3,716,918, issued to Tole, et al. on Feb. 20, 1973. That patent is hereby incorporated by reference in the present specification. Although the denture of the Tole patent represents a significant advance over the preexisting art, there is still room for improvement in the device of the Tole patent. The device of that patent is usually difficult or impossible to insert in the user's mouth when the user's five and six anterior teeth are intact, and especially if the user's bicuspids are also intact. When numerous natural teeth remain in the user's mouth, the deviations of the surfaces of natural teeth and gums from an orientation parallel to the path of insertion can prevent the appliance from being seated successfully if it includes a closed labial flange.
The device of Tole can also be significantly improved when the user's gums are substantially undercut, meaning that a gap remains between the buccal flange of the denture and the buccal surface of the corresponding natural gum when the denture is in place. Food can lodge in this gap. Also, air can enter between the denture and the user's mouth surfaces through this gap, destroying the suction which aids in securing the denture in place. It will be evident that the denture cannot be adapted to fill this undercut by building up the inner surface of the buccal flange of the denture, for that expedient would make the denture impossible to insert in the user's mouth.